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Mootnick and Groves[3] stated that hoolock gibbons do not belong in the genus Bunopithecus, and placed them in a new genus, Hoolock. This genus was argued to contain two distinct species which were previously thought to be subspecies: Hoolock hoolock and Hoolock leuconedys which were later have found that the 2 species have a bigger difference to that of white handed gibbons than bonobos to chimpanzees.[4]

In India and Bangladesh it is found where there is contiguous canopy, broad-leaved, wet evergreen and semi-evergreen forests dipterocarpus forest often mountainous. The species is an important seed disperser; its diet includes mostly ripe fruits, with some flowers, leaves and shoots.[citation needed]

There are numerous threats to western hoolock gibbons in the wild, and are now entirely dependent on human action for their survival. Threats include habitat encroachment by humans, forest clearance for tea cultivation, the practice of jhuming (slash-and-burn cultivation), hunting for food and “medicine”, capture for trade, and forest degradation.[1]

Over the last 30–40 years, western hoolock gibbon numbers are estimated to have dropped from more than 100,000 (Assam alone was estimated to have around 80,000 in the early 1970s) to less than 5,000 individuals (a decline of more than 90%).[5] In 2009 it was considered to be one of the 25 most endangered primates,[6] though it has been dropped from the later editions of the list. [7]